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<H2><A NAME="s7">7.</A> <A HREF="networking-concepts-HOWTO.html#toc7">Dialup Interfaces: PPP</A></H2>

<P>
<A NAME="definition-PPP"></A> 
<A NAME="definition-point-to-point-protocol"></A> 
<A NAME="definition-ppp-daemon"></A> 
When you dial your modem to an ISP, and it connects to their modem,
the kernel doesn't just shove IP packets through it.  There is a
protocol called `Point-to-Point Protocol', or `PPP', which is used to
negotiate with the other end before any packets are allowed through.
This is used by the ISP to identify who is dialed up: on your Linux
box, a program called the `PPP daemon' handles your end of the
negotiation.</P>
<P>
<A NAME="definition-dynamic-ip-address"></A> 
<A NAME="definition-static-ip-address"></A> </P>
<P>Because there are so many dialup users in the world, they usually
don't have their own IP address: most ISPs will assign you one of
theirs temporarily when you dial up (the PPP daemon will negotiate
this).  This is often called a `dynamic IP address', as separate from
a `static IP address' which is the normal case where you have your own
address permanently.  Usually they are assigned by modem: the next
time you dial up, you will probably get a different modem in the modem
pool, and hence a different IP address.</P>

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